1. Field of the Invention
This invention relates to pneumatic tank systems, and in particular to a vertical cylindrical tank system for the storage and transfer of pulverulent or powdered material, such as cement or barite.
2. Description of the Prior Art
Conventional tank systems used for the storage and transfer of pulverulent material, such as powdered cement or barite, in the on shore and off shore petroleum drilling industry, typically utilize systems for aerating and pressurizing the contents of the tank to facilitate unloading of the pulverulent material. One such conventional tank is of the vertical cylindrical type having two equal flanged and dished heads on either end of the vertical cylinder. It normally has inclined slope sheets mounted adjacent the bottom of the tank. Air slides having porous slide plates are mounted between the slope sheets. The powdered material is stored in the tank and rests on the surface formed by the slope sheets and air slides. Pressurized air is directed into the hollow area beneath the air slides and slope sheets, and nipples are provided to admit this air chamber for receiving and distributing pressurized air to the various air slides provided for aerating the material. Aeration of the material resting on the air slides and slope sheets causes it to be in a fluidized state whereby it can be readily discharged under pressure from the tank for transferring the powdered material therefrom.
One problem encountered with such conventional tank systems is the tendency of the powdered material contents to infiltrate or settle into the area of the tank beneath the slope sheets. Thus, unwanted loss of a portion of the powdered material from the upper or storage area may occur. In addition, infiltration of the powdered material into the area beneath the slope sheets may result in the contamination of the aerating system, since the particulate material may readily obstruct the nipples admitting the air to the air slides. Furthermore, such a conventional tank having an area beneath the air slides and slope being filled with air under pressure requires that an inordinate amount of air be utilized in the system. Also, such conventional tanks utilize complex construction to provide support for the slope sheets and to resist the force of accumulated air pressure in the area either above or below the slope sheets and air slides. To avoid damaging the air slides and slope sheets due to potential air pressure differential between the area above and beneath the air slides and slope sheets, conventional tanks attempt to equalize the air pressure in the upper and the lower areas by providing two conduits for permitting air flow in opposite directions. One such conduit requires a filter to prevent the powdered material from entering the lower compartment, and the other conduit includes a differential pressure relief valve for holding a back pressure to force the air from the lower area through the nipples into the upper area to accomplish aeration of the pulverulent material.